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The sequences and activities of RegB endoribonucleases of T4-related bacteriophages.

ABSTRACT: The RegB endoribonuclease encoded by bacteriophage T4 is a unique sequence-specific nuclease that cleaves in the middle of GGAG or, in a few cases, GGAU tetranucleotides, preferentially those found in the Shine-Dalgarno regions of early phage mRNAs. In this study, we examined the primary structures and functional properties of RegB ribonucleases encoded by T4-related bacteriophages. We show that all but one of 36 phages tested harbor the regB gene homologues and the similar signals for transcriptional and post-transcriptional autogenous regulation of regB expression. Phage RB49 in addition to gpRegB utilizes Escherichia coli endoribonuclease E for the degradation of its transcripts for gene regB. The deduced primary structure of RegB proteins of 32 phages studied is almost identical to that of T4, while the sequences of RegB encoded by phages RB69, TuIa and RB49 show substantial divergence from their T4 counterpart. Functional studies using plasmid-phage systems indicate that RegB nucleases of phages T4, RB69, TuIa and RB49 exhibit different activity towards GGAG and GGAU motifs in the specific locations. We expect that the availability of the different phylogenetic variants of RegB may help to localize the amino acid determinants that contribute to the specificity and cleavage efficiency of this processing enzyme.

SUBMITTER: Piesiniene L

PROVIDER: S-EPMC524301 | biostudies-literature | 2004

REPOSITORIES: biostudies-literature

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The sequences and activities of RegB endoribonucleases of T4-related bacteriophages.

Piesiniene Lina L Truncaite Lidija L Zajanckauskaite Aurelija A Nivinskas Rimas R

Nucleic acids research 20041014 18

The RegB endoribonuclease encoded by bacteriophage T4 is a unique sequence-specific nuclease that cleaves in the middle of GGAG or, in a few cases, GGAU tetranucleotides, preferentially those found in the Shine-Dalgarno regions of early phage mRNAs. In this study, we examined the primary structures and functional properties of RegB ribonucleases encoded by T4-related bacteriophages. We show that all but one of 36 phages tested harbor the regB gene homologues and the similar signals for transcrip ...[more]

PMID: 15486207

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Project description:The T4-related bacteriophages are a group of bacterial viruses that share morphological similarities and genetic homologies with the well-studied Escherichia coli phage T4, but that diverge from T4 and each other by a number of genetically determined characteristics including the bacterial hosts they infect, the sizes of their linear double-stranded (ds) DNA genomes and the predicted compositions of their proteomes. The genomes of about 40 of these phages have been sequenced and annotated over the last several years and are compared here in the context of the factors that have determined their diversity and the diversity of other microbial genomes in evolution. The genomes of the T4 relatives analyzed so far range in size between ~160,000 and ~250,000 base pairs (bp) and are mosaics of one another, consisting of clusters of homology between them that are interspersed with segments that vary considerably in genetic composition between the different phage lineages. Based on the known biological and biochemical properties of phage T4 and the proteins encoded by the T4 genome, the T4 relatives reviewed here are predicted to share a genetic core, or "Core Genome" that determines the structural design of their dsDNA chromosomes, their distinctive morphology and the process of their assembly into infectious agents (phage morphogenesis). The Core Genome appears to be the most ancient genetic component of this phage group and constitutes a mere 12-15% of the total protein encoding potential of the typical T4-related phage genome. The high degree of genetic heterogeneity that exists outside of this shared core suggests that horizontal DNA transfer involving many genetic sources has played a major role in diversification of the T4-related phages and their spread to a wide spectrum of bacterial species domains in evolution. We discuss some of the factors and pathways that might have shaped the evolution of these phages and point out several parallels between their diversity and the diversity generally observed within all groups of interrelated dsDNA microbial genomes in nature.

Project description:BackgroundBacteriophages are an important repository of genetic diversity. As one of the major constituents of terrestrial biomass, they exert profound effects on the earth's ecology and microbial evolution by mediating horizontal gene transfer between bacteria and controlling their growth. Only limited genomic sequence data are currently available for phages but even this reveals an overwhelming diversity in their gene sequences and genomes. The contribution of the T4-like phages to this overall phage diversity is difficult to assess, since only a few examples of complete genome sequence exist for these phages. Our analysis of five T4-like genomes represents half of the known T4-like genomes in GenBank.ResultsHere, we have examined in detail the genetic diversity of the genomes of five relatives of bacteriophage T4: the Escherichia coli phages RB43, RB49 and RB69, the Aeromonas salmonicida phage 44RR2.8t (or 44RR) and the Aeromonas hydrophila phage Aeh1. Our data define a core set of conserved genes common to these genomes as well as hundreds of additional open reading frames (ORFs) that are nonconserved. Although some of these ORFs resemble known genes from bacterial hosts or other phages, most show no significant similarity to any known sequence in the databases. The five genomes analyzed here all have similarities in gene regulation to T4. Sequence motifs resembling T4 early and late consensus promoters were observed in all five genomes. In contrast, only two of these genomes, RB69 and 44RR, showed similarities to T4 middle-mode promoter sequences and to the T4 motA gene product required for their recognition. In addition, we observed that each phage differed in the number and assortment of putative genes encoding host-like metabolic enzymes, tRNA species, and homing endonucleases.ConclusionOur observations suggest that evolution of the T4-like phages has drawn on a highly diverged pool of genes in the microbial world. The T4-like phages harbour a wealth of genetic material that has not been identified previously. The mechanisms by which these genes may have arisen may differ from those previously proposed for the evolution of other bacteriophage genomes.

Dataset Information

The sequences and activities of RegB endoribonucleases of T4-related bacteriophages.

Publications

The sequences and activities of RegB endoribonucleases of T4-related bacteriophages.

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